GROWTH-CONTROL OF EMBRYONIC STEM-CELLS INJECTED INTO MOUSE UTERUS ON 5TH DAY OF PREGNANCY

Previous studies have shown that embryonic stem cells (ES) may partici pate in normal embryonic development when they are injected into the b lastocyst. In contrast, ES cells develop into tumors if injected in ec topic sites in adult mice. In this study we injected ES-D3 cells, with the LacZ gene incorporated, into 5-day pregnant mouse uteri, into pre gnant unilaterally salpingectomized uteri, into pseudopregnant uteri a nd into non-pregnant uteri. X-gal staining enabled us to identify inje cted ES cells on the 7th, 9th, 1Oth, 12th and 15th days post-injection . In pregnant decidua, the ES cells were located initially in the meso metrial decidua and later distributed in the basal and capsular decidu a and in the endodermic layer of the visceral yolk sac. In pregnant, u nilaterally salpingectomized mouse uteri, ES cells were mainly located in the uterine lumen and tumors were not observed in either case. In contrast, ES cells injected into pseudopregnant uteri often developed into tumors and those injected into non-pregnant uteri always develope d into teratocarcinomas. We conclude that the pregnant-uterine microen vironment may participate in the control of ES cell growth. (C) 1994 W iley-Liss, Inc.